Patch 5.4 - Proving Grounds Preview
There are a few things we know so far:

Items are scaled to item level 463, but gems are not scaled down. Set bonuses don't work.

Flasks and food buffs are allowed, but potions are not. You also get a full set of raid buffs.

The UI elements (timers and wave counters) and audio were not in in the videos below.

The DPS video below just shows Gold for DPS, stopping a few waves before the end. This is a somewhat older version of Gold, the current version on the PTR is significantly easier.

Originally Posted by Blizzard
(Blue Tracker / Official Forums)

There comes a time in any healer, tank, or damage dealer’s life when they decide to take their collaborative skills and abilities to the next level. When that time comes, the Proving Grounds will be waiting. Set within the Temple of the White Tiger, this new feature will provide a repeatable solo Scenario where level 90 players can test their mettle or try out different roles in a safe, controlled environment.

Getting In
To get started, you’ll need to talk with an NPC in the Temple of the White Tiger in Kun-Lai Summit or class trainer, who'll grant you entrance to the instance. Upon entering the Proving Grounds, your gear will be scaled down much like it is in Challenge Modes. Depending on the role you choose, you may not have to go it alone. (Then again, you just might. Aren’t you brave?)

Choose Your Role
Within the Proving Grounds, much like in any dungeon, you’ll be able to choose the role of tank, DPS, or healer. Once you’ve decided, you’ll be faced with a series of challenges based on the kinds of combat mechanics that role would encounter in a dungeon.

Tank: You will be tasked with protecting an NPC from oncoming waves of enemies, which will test your tanking skills in various ways. Fear not, though a friendly NPC will assist, by healing you, and damaging the enemies.

Damage: Sometimes you just have to go it alone. You'll melt the usual faces, while handling a variety of mechanics including interrupting heals, chasing down runners, timing cooldowns, avoiding harmful mechanics, and more.

Healer: Four NPCs will join you to form a full party. It will take a special healing touch to keep your friendsalive, as you work together to face the challenges of attacking enemies.

Choose Your own Adventure
Proving Grounds will be available in four different modes: Bronze, Silver, Gold, and Endless. Each mode allows you the opportunity to test your mettle and learn a bit more about your role by putting you in the thick of a grouping experience. You’ll have to beat each one (beginning with Bronze) to take on the next mode. Once you’ve beaten Gold, you’ll unlock Endless and be truly prepared to astound and amaze your friends with your prowess.

In Endless, you’ll push yourself to the limits and see just how long you can survive as each wave of foes becomes more and more difficult to withstand. The longer you survive Endless, the higher your score, and the system will track your progress so you can see just how well you’ve done.

Choose to Endure
You’ll be able to reenter the Proving Grounds as much as you want as you work to improve your skills earn Achievements, and claim some bragging rights when you survive longer than any of your friends. It’s just a quick chat with the NPC, and you're quickly back in action.

You won’t need to worry about death or taking durability damage. Food and flasks will last their full duration, but leave your potions at home – you won’t be able to use them here. You’ll also have access to various amenities within the Proving Ground such as Vendors, Runeforges, Soulwells, repairs, and Reforgers.

Now that you know what’s in store, sharpen those blades, enchant that new robe, and get ready to go boldly into the Proving Grounds.

Frostflame WeaponIncreases the damage of your Lava Lash by 40% if your off-hand weapon is enchanted with Frostbrand.While your weapon is imbued with Flametongue Weapon, your attacks also slow the target's movement speed by 50% for 3 sec.

Item - Death Knight T16 DPS 4P Bonus Death Coil increases the duration of Dark Transformation by 2.0 sec per cast. Pillar of Frost increases rune regeneration speed by 50% while active.Special attacks while Pillar of Frost is active will impale your target with an icy spike.

Item - Druid T16 Balance 4P BonusEvery time you enter Solar or Lunar Eclipse, the cooldown of Celestial Alignment is reduced by 5 sec.Your chance to get Shooting Stars from a critical strike from Moonfire or Sunfire is increased by 20%.

Item - Monk T15 Windwalker 4P BonusYou have a 10% chance to gain an additional charge of Tigereye Brew every time you gain a charge of Tigereye Brew.Increases the damage of your Tigereye Brew by 1% per stack consumed.

Item - Warlock T16 4P Bonus When a Burning Ember fills up, your critical strike chance is increased by 15% for 5 sec. Haunt has a 8%10% chance to refund its shard when expiring. Shadow Bolt and Touch of Chaos have a 8% chance to also cast Hand of Gul'dan at the target.

Malice Fires Malicious Blast at the closest 2 allies every 1.52 sec. Any Malicious Blast that is not absorbed will be fired at Garrosh instead, granting him 5 Energy. Limited to 1 target. Unlimited range. Instant.

Mark of Arrogance Marks an enemy, causing them to suffer 55,00070,000 Shadow damage every second for the remainder of the fight. This effect stacks. Removing this effect gives the dispeller 5 Pride. Limited to 2 targets. Instant.

Projection Causes an enemy's pride to project at a nearby location. The projection explodes, inflicting 175,000225,000 Shadow damage to all players after 8 seconds unless the creator of the projection is standing within it. 200 yd range. Instant.

Return to Stone Drains some of the life essence from players, inflicting 100,000 Shadow damage and creating stone statue copies of those players. These statues frequently strike the ground, inflicting 200,000150,000 Physical damage and stunning targets in a frontal cone for 2 sec. These statues remain until killed. 1 sec cast.

Set to Blow Throws a pack of highly volatile bombs on the back of players. After 30 sec, these bombs will detonate, inflicting 200,000 Fire damage per remaning stack to all players within 10 yards. Players may use Throw Bomb to remove one of these bombs, dropping it on the ground instead. Bombs on the ground will detonate for 200,000 Fire damage when any player enters their proximity or after 30 sec. The damage from any of these bombs can chain to nearby ground bombs. Unlimited range. 2 sec cast.1 sec cast.

Oh good...they're not going to gate the Proving Grounds with a required ilvl. I was scared for that. I reall can't wait to try out the healing aspect of that feature. It's about time they gave healers a chance to actually use their heals in a solo scenario/fight-type thing w/o needing to have a DPS spec or put out nasty amts of DPS as a healer. WOOO!

Down to 3 Chi from 4 so you acquire it faster...
Use Tigereye Brew to consume the charges, granting you 6% increased damage and healing for 15 sec. which is up from 5%...
You can only consume up to 15 stacks at a time for 90% increased damage up from 75%...

Seems like they buffed it a little bit. Granted the whole spec and class needs much more than that but I don't see how it's a nerf.

Bronze mode - Average to Above average players will find this challenging but not impossible. Passing through Bronze mode will give you the stamp of approval for normal mode raiding guilds

Silver mode - Almost impossible to complete without playing your class perfectly. Average players will hit a brick wall here and above average players will really struggle here. Still not impossible but requires perfect play. PvP heroes and casual 5 man heroic players will not succeed until they get better at the game. Even the most hardcore of players will need a good few hours of wiping before finishing. Wiping here is nothing to be embarrassed about

Gold - Impossible. No one will succeed here for a few weeks. Requires insane play that only the best are capable of. Takes days of wiping to even pass the first wave. Once you know the encounter inside out and have a solid strategy down can you start to progress through the waves of mobs. Will include a metric shit ton of one shot mechanics. If you stand in the wrong place at any time during this encounter you will be killed instantly. Getting Gold is an impressive achievement and will earn you celebrity status on your realm.

Endless mode - Endless mode is insanely difficult. Only the best of the best of the best can do well here. Where getting Gold mode shows that you are one of the best, Endless mode shows you ARE the best. Each time you enter, the encounter changes randomly so you can't learn a strategy and get some addon that tells you what to do. This relies on pure instinct and draws upon your full experience as a WoW player. One wrong move and your dead. Even the most advanced players in WoW will fail here as they are used to watching a boss mod timer to know when to do stuff. For this you not only need to play your class like a God you also need lightning fast reactions to adjust to the ever changing encounter.

Bronze mode - Average to Above average players will find this challenging but not impossible. Passing through Bronze mode will give you the stamp of approval for normal mode raiding guilds

Silver mode - Almost impossible to complete without playing your class perfectly. Average players will hit a brick wall here and above average players will really struggle here. Still not impossible but requires perfect play. PvP heroes and casual 5 man heroic players will not succeed until they get better at the game. Even the most hardcore of players will need a good few hours of wiping before finishing. Wiping here is nothing to be embarrassed about

Gold - Impossible. No one will succeed here for a few weeks. Requires insane play that only the best are capable of. Takes days of wiping to even pass the first wave. Once you know the encounter inside out and have a solid strategy down can you start to progress through the waves of mobs. Will include a metric shit ton of one shot mechanics. If you stand in the wrong place at any time during this encounter you will be killed instantly. Getting Gold is an impressive achievement and will earn you celebrity status on your realm.

Endless mode - Endless mode is insanely difficult. Only the best of the best of the best can do well here. Where getting Gold mode shows that you are one of the best, Endless mode shows you ARE the best. Each time you enter, the encounter changes randomly so you can't learn a strategy and get some addon that tells you what to do. This relies on pure instinct and draws upon your full experience as a WoW player. One wrong move and your dead. Even the most advanced players in WoW will fail here as they are used to watching a boss mod timer to know when to do stuff. For this you not only need to play your class like a God you also need lightning fast reactions to adjust to the ever changing encounter.

That kind of misses the point of their purpose. They're supposed to teach, not be murderous.

Down to 3 Chi from 4 so you acquire it faster...
Use Tigereye Brew to consume the charges, granting you 6% increased damage and healing for 15 sec. which is up from 5%...
You can only consume up to 15 stacks at a time for 90% increased damage up from 75%...

Seems like they buffed it a little bit. Granted the whole spec and class needs much more than that but I don't see how it's a nerf.

Some people have no clue how to read patch notes or tell what is a Nerf or not. Half the timee they see red there is nerfs.

Bronze mode - Average to Above average players will find this challenging but not impossible. Passing through Bronze mode will give you the stamp of approval for normal mode raiding guilds

Silver mode - Almost impossible to complete without playing your class perfectly. Average players will hit a brick wall here and above average players will really struggle here. Still not impossible but requires perfect play. PvP heroes and casual 5 man heroic players will not succeed until they get better at the game. Even the most hardcore of players will need a good few hours of wiping before finishing. Wiping here is nothing to be embarrassed about

Gold - Impossible. No one will succeed here for a few weeks. Requires insane play that only the best are capable of. Takes days of wiping to even pass the first wave. Once you know the encounter inside out and have a solid strategy down can you start to progress through the waves of mobs. Will include a metric shit ton of one shot mechanics. If you stand in the wrong place at any time during this encounter you will be killed instantly. Getting Gold is an impressive achievement and will earn you celebrity status on your realm.

Endless mode - Endless mode is insanely difficult. Only the best of the best of the best can do well here. Where getting Gold mode shows that you are one of the best, Endless mode shows you ARE the best. Each time you enter, the encounter changes randomly so you can't learn a strategy and get some addon that tells you what to do. This relies on pure instinct and draws upon your full experience as a WoW player. One wrong move and your dead. Even the most advanced players in WoW will fail here as they are used to watching a boss mod timer to know when to do stuff. For this you not only need to play your class like a God you also need lightning fast reactions to adjust to the ever changing encounter.

wont happen, you get achive for clearing 30 waves on endless mode = 30 first waves endless mode will be easy so everyone can get their achiv and title